The use of increasingly high speed integrated circuits (ICs) in computer systems has given rise to new assembly challenges related to the attachment and support of the ICs. Due to the large, thermally induced stresses that impact the long term reliability of solder joints, high speed, high density IC module assemblies can not employ standard solder techniques for connecting modules to a circuit board. Therefore, interposer socket assembly techniques, specifically land grid array (LGA) sockets, have emerged as a substitute for solder joints.
An LGA socket is placed on the circuit board and makes electrical contact with the circuit board through a plurality of input/output (IO) interconnects. An IC module is placed on the LGA socket in electrical contact so that the LGA socket enables electrical connection between the IC module and the circuit board. Assemblies using LGA sockets require mechanisms for applying compressive load on the assembly such that the LGA socket establishes and maintains reliable electrical connection with the circuit board, thereby ensuring reliable electrical connection between the IC module and the circuit board.
Coil spring assemblies are widely used in the art for applying a compressive load on LGA assemblies. Typically, a coil spring assembly includes an anchor screw, a spring, one or more washers to eliminate metal debris and a clip to capture the screw to a heat sink. The spring may be compressed as the anchor screw is tightened. The coil spring assemblies may be located along the perimeter of the LGA assembly. Compressive load is derived from the coil spring assemblies and spread across a heat sin and applied to the LGA assembly.
Prior art systems utilizing coil spring assemblies are limited. Large loads are difficult to achieve with load systems utilizing coil spring assemblies. Systems using coil spring assemblies are also difficult to manufacture. The anchor screw of each coil spring assembly must be tightened to apply a compressive load. Each anchor screw must be tightened individually before moving on to another anchor screw located in a corresponding opposite direction. In order to apply an even compressive load on the LGA assembly, the anchor screws must be sequentially tightened in a series of repetitive steps performed in a cross pattern configuration. Typically, three or more repetitions of each cross pattern are required. For example, if four coil spring assemblies are used in a system, twelve or more repeated operations may be required. Additionally, systems using coil spring assemblies are susceptible to unevenly applied loads on the LGA socket. Transverse loads may be created that interfere with the alignment of the processor to the LGA socket. Further, conventional coil spring assemblies typically involve a high part count. For example, a coil spring assembly may comprise a screw, a spring, one or more washers and a clip to capture the screw to a heat sink. The increased part Count may result in increased assembly time and costs. Further, systems using coil spring assemblies suffer from impeded thermal performance. Typically, a heat sink is used to dissipate heat generated by the IC module. The heat sink typically comprises a plurality of fins exposed to the ambient air. In order to make space for the coil spring assemblies (i.e. footprint), a significant amount of fin area must be removed from the heat sink, thereby reducing the performance of the heat sink. The coil spring assemblies may also create an obstruction to airflow in the heat sink.